1. Technical Field
This application relates to a dual mode mobile telecommunication device in general (for instance a UMTS (Universal Mobile Telecommunications System) and GSM (Global System for Mobile Communications) dual mode device), and to an apparatus and method for selecting cells in mobile telecommunications system user equipment. The invention also relates to Mobile Stations (MS) and User Equipment (UE) which support at least two Radio Access Technologies (RATs).
2. Description of the Related Art
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In a typical cellular radio system, mobile user equipment (UE) communicates via a radio access radio network (RAN) to one or more core networks. User equipment (UE) comprises various types of equipment such as mobile telephones (also known as cellular or cell phones), lap tops with wireless communication capability, personal digital assistants (PDAs) etc. These may be portable, hand held, pocket sized, installed in a vehicle etc and communicate voice and/or data signals with the radio access network.
The radio access network covers a geographical area divided into a plurality of cell areas. Each cell area is served by at least one base station, which may be referred to as a Node B. Each cell is identified by a unique identifier which is broadcast in the cell. The base stations communicate at radio frequencies over an air interface with the UEs within range of the base station. Several base stations may be connected to a radio network controller (RNC) which controls various activities of the base stations. The radio network controllers are typically connected to a core network.
UMTS is a third generation public land mobile telecommunication system. Various standardization bodies are known to publish and set standards for UMTS, each in their respective areas of competence. For instance, the 3GPP (Third Generation Partnership Project) has been known to publish and set standards for GSM (Global System for Mobile Communications) based UMTS, and the 3GPP2 (Third Generation Partnership Project 2) has been known to publish and set standards for CDMA (Code Division Multiple Access) based UMTS. Within the scope of a particular standardization body, specific partners publish and set standards in their respective areas.
Consider a wireless mobile device, generally referred to as user equipment (UE), that complies with the 3GPP specifications for the UMTS and with GSM protocols. The 3GPP 25.331 specification, v.3.18.0, referred to herein as the 25.331 specification, addresses the subject of the Radio Resource Control (RRC) protocol specification. The 3GPP 25.304 specification, v.3.14.0, referred to herein as the 25.304 specification, addresses the subject of UMTS User Equipment (UE) procedures in idle mode and procedures for cell reselection in connected mode between the UMTS Terrestrial Radio Access Network (UTRAN) and the UE.
Such a UE undertakes frequent measurement procedures. Clause 8.4 of the 25.331 standard and its sub-clauses and clause 14 and its sub-clauses relate to the measurement procedures to be undertaken by the UE as do clause 5 and its sub-clauses of the 25.304 specification. Both the 25.331 standard (and in particular clause 8.4 and its sub-clauses and clause 14 and its sub-clauses) and the 25.304 standard (and in particular clause 5.2.3.1 and its sub-clauses) are incorporated herein by reference.
When camped on a UMTS cell, the UE shall regularly search for a better cell according to the cell reselection criteria. If a better cell is found, the UE should attempt to select that cell. A change of cell may imply a change of RAT.
The 3GPP specifications allow a dual-mode UE to repeatedly attempt to camp on a cell using another RAT when the cell is known to be unavailable just because it happens to have the strongest available transmission signal.
For a dual-mode UE operating in UMTS idle mode (or CELL_PCH, URA_PCH or CELL_FACH states) and a GSM cell is initially found to be the best cell, problems can arise if the GSM cell is unsuitable or unavailable for selection, for example, if synchronization cannot be achieved or system information cannot be decoded. Each unsuccessful attempt to reselect to the unsuitable/unavailable GSM cell results in a short loss of service, and the UE will be unresponsive to attempts at incoming communication. It will therefore be seen that there is a need to avoid such repeated interruptions.
Further, battery power in the UE can also be wasted by repeated attempts of the UE to change its operational mode between RATs every few seconds. With reference to clause 5.5.2.2.3 of the 3GPP 25.133 specification, v 3.18.0, the minimum interruption time when attempting to move from a UMTS cell to a GSM cell is 40 ms, and is likely to be considerably longer, perhaps even greater than 100 ms.
There are thus proposed strategies for User Equipment (UE) measurement procedures, which are appropriate in UMTS idle mode and during cell reselection to a GSM cell. A number of such strategies are detailed below.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of an apparatus and method for carrying out User Equipment (UE) procedures in idle mode and procedures for cell reselection in connected mode.
The same reference numerals are used in different figures to denote similar elements.